Dredging operations require that the waterway bottom materials and spoils be disturbed and removed. Such disturbing of the waterways bottom produces turbidity, and in many instances excessive turbidity has an adverse environmental effect and standards for acceptable turbidity conditions during dredging have been established by the Department of Army, Corps of Engineers, Departments of Natural Resources and Environmental Protection Agencies responsible for dredging and marine construction operations.
In many dredging operations it is desirable to use high pressure water jets directed toward the bottom surface to be removed, wherein such jetting or agitation loosens and disintegrates the bottom material to facilitate removal by suction pumps. While dredging operations utilizing jet nozzles are capable of high volume removal of spoils and bottom material, the nature of a jetting operation produces high turbidity conditions with conventional dredging apparatus. Accordingly, in those areas wherein turbidity must be closely controlled, and with minimal tolerance, dredging operations may become excessively expensive and time consuming due to turbidity control requirements. The problem is particularly critical where the bottom sediments contain heavy metals and toxic wastes.
In my U.S. Pat. No. 3,971,148 I disclose the use of a hood having fixed and movable portions to reduce turbidity, but this apparatus does not employ jets and the relatively open cutter head apparatus is incapable of reducing the turbidity to the levels often presently required, especially at high material removing rates.
It is also known to use jet nozzles in dredging operations of the suction type as shown in U.S. Pat. Nos. 501,870 and 3,412,862, and while such disclosures show the use of water jets engaging the material to be removed prior to entering a dredge head or housing, the known prior art using jets has not been concerned with turbidity control, and to the inventor's knowledge, jet dredging apparatus is not available capable of effectively controlling turbidity while dredging at high volumes of spoil removal, particularly when dredging spoils containing matter conducive to producing high turbidity.
It is an object of the invention to provide a method and apparatus for controlling and minimizing turbidity during dredging operations.
It is another object of the invention to provide a dredging turbidity control system wherein various aspects of the dredging operation may be regulated to minimize turbidity.
A further object of the invention is to provide a suction type dredging system capable of utilizing high pressure jets to loosen and agitate the material to be dredged, and yet reduce turbidity to environmentally acceptable levels.
Another object of the invention is to provide a turbidity control system for dredging operations wherein the degree of turbidity may be automatically determined, and wherein dredge head components and operations may be controlled in accordance with the turbidity conditions to maintain turbidity within acceptable levels and permit the most efficient operation of the dredging apparatus which is environmentally permissible.
An additional object of the invention is to provide dredging apparatus mounted upon a barge utilizing a turbidity sensor wherein the sensor may automatically regulate control means for varying the pressure and volume of water jets, varying the flow area entering the dredge head, regulating the volume of water being drawn from the dredge head, and regulating the rate of advancement of the barge and head wherein dredging conditions may be optimized while maintaining turbidity within low acceptable levels.
In the practice of the invention the dredging apparatus includes a barge from which suspends a dredge head. The dredge head is of the suction type wherein a powerful pump mounted upon the barge or dredge ladder draws water and the dredged material from the head and discharges into a conduit for depositing the pumped material to a remote location.
The dredge head consists of a housing having a rear wall, an upper wall and a front face open in the direction of head advance. Preferably, the lower portion of the head is also open, and powered rotating cutter elements are mounted within the head having a plurality of rotating knives defined thereon for agitating and cutting through the water bottom material or spoils to break up the bottom material permitting the same to be drawn into the dredge head suction conduit.
At the upper region of the dredge head, a hood is pivotally mounted and positionable by a hydraulic cylinder wherein the hood extends forward of the head open face and may be pivoted toward or away from the head face to vary the flow area into the dredge head and thereby regulate the velocity and direction of the water entering the head. Further, a plurality of jet nozzles are mounted upon the forward edge of the hood which are disposed downwardly and are connected to a source of pressurized water located on the barge.
The jet nozzles discharge downwardly for agitating and breaking up the bottom material directly ahead of the dredge head, and moving the bottom material into the head. Depending upon the pivotal position of the hood, the jets are directed a greater or lesser distance in front of the dredge head, and operation of the hydraulic hood positioning power means permits close control of the positioning of the jet nozzles.
As the dredge head is closed at its rear wall, top and sides, and as the open bottom is engaging the material being removed, water may enter the head only through the front face. This flow path contrasts with that of my U.S. Pat. No. 3,971,148 which was relatively open at the rear. By limiting the water flow into the head through the front face the velocity and volume of the water entering the head can, to a significant extent, be controlled by the position of the hood, and under high turbidity conditions "closing" of the hood will confine the turbid water adjacent the head front face wherein it will be drawn into the head.
Control means are mounted upon the barge for controlling the position of the hood, the pressure of the water being supplied to the jets, the rate that water and spoils are removed from the dredge head, the rate of advancement of the barge, and other functions wherein these operations may be simultaneously or individually regulated and adjusted.
A sensor is mounted adjacent the dredge head for accurately determining the turbidity conditions existing at the head. Such a sensor is of conventional type utilizing a light source for determining the reflective characteristics of the water, and hence the degree of turbidity at any given time.
Preferably, the sensor automatically controls the aforementioned control means, and under excessive turbidity conditions, the position of the hood and jets, the amount of water being expelled from the jets, the rate of removal of the water from the head, or the rate of advancement of the barge and dredge head can be automatically regulated to produce optimum operating efficiencies within turbidity parameters.
The practice of the invention permits turbidity regulations to be met while permitting the dredging of bottom material to take place at a cost effective rate, and the invention permits the suction dredging of bottom compositions which could not heretofore be efficiently dredged within turbidity limitations.